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The Swedish two-county trial of mammographic screening: Cluster randomisation and end point evaluation
Queen Mary University of London, London, United Kingdom.
Falun Central Hospital, Falun, Sweden.
Östergötlands Läns Landsting, Centre for Medical Imaging, Department of Radiology UHL.
Queen Mary University of London, London, United Kingdom.
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2003 (English)In: Annals of Oncology, ISSN 0923-7534, E-ISSN 1569-8041, Vol. 14, no 8, 1196-1198 p.Article in journal (Refereed) Published
Abstract [en]

Background: The Swedish Two-County Trial has been criticised on the grounds of the cluster randomisation and alleged bias in classification of cause of death. Patients and methods: In the Two-County Trial, 77080 women were randomised to regular invitation to screening (active study population, ASP) and 55985 to no invitation (passive study population, PSP), in 45 geographical clusters. After ~7 years, the PSP was invited to screening and the trial closed. We analysed data using hierarchical statistical models to take account of cluster randomisation, and performed a conservative analysis assuming a systematic difference between ASP and PSP in baseline breast cancer mortality in one of the counties. We also analysed deaths from causes other than breast cancer and from all causes among breast cancer cases diagnosed in the ASP and PSP. Results: Taking account of the cluster randomisation there was a significant 30% reduction in breast cancer mortality in the ASP. Conservatively, assuming a systematic difference between ASP and PSP clusters in baseline breast cancer mortality, there was a significant 27% reduction in mortality in the ASP. Ignoring classification of cause of death, there was a significant 13% reduction in all-cause mortality in breast cancer cases in the ASP. Conclusions: Breast cancer mortality is a valid end point and mammographic screening does indeed reduce mortality from breast cancer. The criticisms of the Swedish Two-County Trial are unfounded.

Place, publisher, year, edition, pages
2003. Vol. 14, no 8, 1196-1198 p.
Keyword [en]
Breast screening, Mammography, Randomised trial
National Category
Natural Sciences
URN: urn:nbn:se:liu:diva-46529DOI: 10.1093/annonc/mdg322OAI: diva2:267425
Available from: 2009-10-11 Created: 2009-10-11 Last updated: 2012-01-07

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